Method of producing a bronze finish on copper and copper alloys



Patented Dec. 15, 1936 METHOD OF PRODUCING A BRONZE FINISH ON COPPER ANDCOPPER ALLOYS John B. Freeman, Jr., Cheshire, and Rollo L. Hunger-ford,Waterbury, Conm, assignors to The American Brass Company, Waterbury,Conn., a corporation of Connecticut No Drawing. Application November 10,1934,

This invention relates to copper and copper alloys, and has for anobjectto provide an improved method of producing a bronze finish oncopper or copper alloys so as to give articles 5 made of such materialsa weathered bronze appearance in a short time.

We are aware of the patent to Laist el al No. 1,428,170 grantedSeptember 5, 1922 in which is disclosed a process for coloring metalliccop 10 per to secure a colored surface of various shades of green andblue, byimmersing the copper article in a solution of copper nitrate andcopper chloride, and then washing and treating with various solutions tomake the colored coating 15 more adherent and less soluble.

In our process, however, we do not wish a colored coating, but secure arich weathered bronze surface appearance which is very attractive.

20 In carrying out our method the articles of copper or copper alloy arecleaned free from scale, grease, dirt, or any similar surfaceimperfection. We then immerse the article in a hot concentrated solutionof copper nitrate,

25 or otherwise subject it to the action of such solution, for such aperiod of time as experience has shown to be desirable. This isordinarily from about five minutes to a half hour, depending on thetemperature of the solution and the 30 alloy used, ordinarily about 15minutes with a solution temperature of 80 to 90 C. has proven verysatisfactory. The specimen is now washed in hot water, preferably at atemperature of about 80 to 100 C., and the specimen is then i5 dried.The specimen now has upon its surface a roughly adhering green saltconsisting of basic copper nitrate under which is a hard adherentsurface film of a mixture of cuprous and cupric oxides which has adesirable weathered 40 bronze appearance.

We have found that this green loosely adhering layer of basic salt canbe readily removed by a buffing operation which also gives to theunderlying surface film of cupric and cuprous 45 oxides a fine bronzesheen. The bufling operation is preferably performed with a soft clothThis process produces a very beautiful weat h,

ered bronze appearance on copper and copper 50 alloys, and has beenfound to give a particularly desirable appearance on such copper alloysas the silicon bronzes of the so-called Everdur Serial No. 752,476

4 Claims. 148-6) type. such for example as those containing-from about.1 to 10% silicon and up to 4 or 5% manganese, and similar alloys. Itis, however, not confined to such alloys, but is adapted for treatingcopper and copper alloys in general. 5

Having thus set forth the nature of our invention, what we claim is:

1. A method of producing a weathered bronze coating p5 finish onarticles of copper and copperalloys which comprises immersing thearticle in a'hot concentrated solution. of predominantly copper nitrateto form on the metal a surface film of copper oxide under copper salts,washing in hot water to loosen the copper salts, drying, and thenbufiing the surface in such manner as to remove the salts and impart tothe oxide film a weathered bronze appearance.

2. A method of producing a weathered bronze coating or finish onarticles of copper and copper alloys comprising subjecting the articleto the actionof a hot concentrated solution of predominantly coppernitrate to form a surface film of copper oxide and adhering coppersalts, washing the article in hot-'water to loosen the copper salts andthen drying, and then bufilng the surface in such manner as to removethe salts and impart a bronze finish to the copper oxides.

3. In a method of producing a weathered bronze coating or finish onarticles of copper and copper alloys, the steps which consist insubjecting the article to the action of a hot concentrated solutionpredominantly of copper nitrate to produce thereon a coating of a greensalt overlying a surface film of copper oxides, washing in hot water toloosen the green salt and drying, and then buffing the surface in suchmanner as to remove the colored salts and impart a bronze finish to theoxides.

4. A method of producing a weathered bronze 40 coating or finish onarticles of copper and copper alloys comprising, cleaning the articleand subjecting it to a hot concentrated solution of' predominatelycopper nitrate for a sufiicient time to produce on its surface a roughlyadhermg salt of basic copper nitrate over a surface film of copperoxides, then washing the article in hot -wate r. to loosenthesal-tanddrylng, and buffing the surface to remove the. salt andimpart a bronze finish to the oxide film.

' JOHN R. JR.

ROLLO L. HUNGER-FORD.

